The present invention relates to equipment and techniques for performing workover or snubbing operations commonly carried out in the oil and gas recovery industry. In particular, the present invention relates to an improved snubbing unit which allows tubular members to be run and rotated more efficiently than hereto known in the art.
In oil and gas recovery operations, tubular members are usually run or pulled using a workover rig or a snubbing unit. Workover rigs are in essence small drilling rigs having a derrick and draw works. While workover rigs are less expensive and time consuming to employ than full sized drilling rigs, use of workover rigs can still be quite costly. Snubbing units are smaller, easier to transport and less expensive to operate than workover rigs. Moreover, snubbing units are often employed when working a pressurized well which requires the tubular members be forced into the well bore. A snubbing unit typically consists of a raised platform with two or more slip assemblies positioned beneath the platform. A typical prior snubbing unit is disclosed in U.S. Pat. No. 4,085,796 to Council. Often the raised platform of the snubbing unit will include a railed work area or xe2x80x9cbasketxe2x80x9d such as seen in U.S. Pat. No. 4,085,796. The two or more slip assemblies will be operated to run or pull tubulars as is well known in the art. Workmen will occupy the basket to assist in running or pulling the tubulars and will normally employ a power tong and a back-up tong in the basket to makeup or break apart a string of tubulars.
It is often desirable during snubbing operations to rotate the tubular member. While units such as in U.S. Pat. No. 4,085,796 do not provide a method for applying torque to the tubular, other snubbing units such as that seen in U.S. Pat. No. 5,746,276 to Stuart do. U.S. Pat. No. 5,746,276 shows the typical snubbing unit having an upright structure with two slip assemblies positioned within the structure and a back-up tong positioned atop the structure. However, the entire structure is further positioned upon a rotary table. When it is desired to rotate the tubular member, the tong grips the tubular member and the entire structure spins on the rotary table. It will be understood that the snubbing units as shown in the above patents must additionally utilize a power tong and back-up tong combination to makeup and break apart joints on the string of tubulars being run. Most commonly, the power tong and back-up combination will be suspended from a cable and hang in inside the basket such as to be accessible by workmen. Alternatively, the power tong and back-up tong combination could connected to the structure of the snubbing unit itself. However, when tongs are connected to the rotary table such as suggested in Stuart, the power tong and back-up tong combination must rotate within the basket.
There are serious disadvantages in the manner which the prior art snubbing units apply torque to the tubular. First, while many snubbing units may incorporate a rotary table, often these snubbing units do not have a back-up tong gripping the tubular as seen in Stuart. Rather, the snubbing unit relies on the gripping force of the slips in order to transfer torque from the rotary table to the tubular. However, slips are primarily designed to hold the tubular against vertical movement and may not securely hold the tubular against rotary movement. Therefore, applying torque with slips often results in slippage between the tubular and the slips, causing serious and damaging scaring of the tubular surface.
Second, it is inherently inefficient to utilize two torque producing tools in a single snubbing unit. Existing snubbing units use a rotary table to apply torque to the entire drill string, but also must use a power tong to apply torque to a tubular joint being made-up or broken apart. It would be a more efficient system to use a single torque source, either the rotary table or the power tong, to perform both tasks. A single torque source would reduce the cost, weight, and overall size of the snubbing unit.
Third, rotating the entire slip assembly and tongs attached thereto creates a hazardous work environment. The workmen in the basket must have access to the power and back-up tongs when they are not rotating. However, if the tongs are rotating in conjunction with the slips and tubular string, the tongs could seriously injure a workman who inadvertently places a limb in the circumference of the rotating tongs. The snubbing unit""s basket would be a far safer work environment if the power and back-up tongs did not rotate when torque is applied to the tubular string.
It is therefore an object of the present invention to provide a snubbing unit which may apply torque to a tubular string without scarring or otherwise damaging the tubulars.
It is another object of the present invention to provide a snubbing unit which may apply torque to the tubular string and makeup/break apart tubulars using the same torque source.
It is still another object of the present invention to provide a safer snubbing unit by eliminating the necessity of rotating the power and back-up tongs when applying torque to the tubular string.
Therefore the present invention provides a snubbing unit drilling system which will include a power tong, a back-up tong, and a mounting structure having a rotating slip assembly positioned on the mounting structure, such that the rotating slip assembly may rotate relative to the mounting structure. A plurality of support legs will be attached between the power tong and the mounting structure such that the support legs prevent relative rotation between the power tong and the mounting structure.